Linear algebra is a widely used tool in computer science and cryptography is no exception to this rule. One notable difference is that in cryptography and cryptanalysis, we mostly consider linear algebra over finite fields (or sometimes rings). Compared to linear algebra over real or complex numbers, there are two essential changes. One for the best: no stability problems can occur; one for the worst: the notion of convergence is no longer available. This makes linear algebra in cryptanalysis quite different from linear algebra for scientific computing. The reader interested in the scientific computing aspect of linear algebra may refer to [GL96].